Syringe with self-returnable plunger

ABSTRACT

A plunger-type syringe is provided in which the plunger returns after it is depressed. The syringe includes an elastic membrane which is received by the tubular barrel and interposed between the barrel and the plunger. A portion of the membrane is secured to the end of the barrel and is thereby restrained against longitudinal movement, and another portion is engagable with the plunger for longitudinal movement therewith within the barrel. As the plunger is depressed, the membrane is stretched and provides a force tending to return the plunger to its original position. When the plunger is released, the elastic membrane returns the plunger.

I United States Patent [151 3,661,152 Beich et al. 1 May 9, 1972 s41 SYRINGE WITH SELF-RETURNABLE FOREIGN PATENTS OR APPLICATIONS PLUNGER 84,542 3/1965 Francem. 128/218 72 Inventors: Frank R Beich, winmette; Glenn L- Bea-u, l,l76,465 7/1959 France ..l28/2 l 8 h Gurnee bot of Primary Examiner-R1chard A. Gaudet [73] Assignee: American Hospital Supply Corporation, ASSiSlan! xa as Evanston, 11] Att0rney-Dawson, Tilton, Fallon & Lungmus [22] Filed: May 8, 1970 57 ABSTRACT PP 35,846 A plunger-type syringe is provided in which the plunger returns after it is depressed. The syringe includes an elastic membrane which is received by the tubular barrel and inter- [52] U.S. Cl ..128/235, 128/218 PA posed between the barrel and the plunger A portion of the [51] 1/00 membrane is secured to the end of the barrel and is thereby Flak! of Search 3 3 1 restrained against longitudinal movement, and another por- 128/213, DIG. 5, 276; 222/336, 337, 338, 339, 340 tion is engagable with the plunger for longitudinal movement therewith within the barrel. As the plunger is depressed, the 56 References Cited membrane is stretched and provides a force tending to return the plunger to its original position. When the plunger is UNITED STATES PATENTS released, the elastic membrane returns the plunger.

1,476,946 12/1923 Bessesen ..222/340 12 Claims, 15 Drawing Figures H1 y Z3- i 1 J2 0 z? ZJ [34. Z .9 4. J7 T P v 31 l J5 7 3.? I 4 '1 l PATENTEDIMY 9 I972 8,661,152

sum 2 [1F 2 This invention relates to syringes, and, more, particularly, to piston-type syringes suitable for medical use.

The invention finds particular utility in medical irrigation syringes but is not limited to that'particular type of syringe. Irrigation syringes, which may be used in irrigating incisions, wounds, body passages, wet dressings or the like, are generally of two types the'piston-type or the bulb-type. A pistonsyringe includes a barrel and a piston or plunger which is slidable longitudinally within the barrel to eject fluid from the barrel or to draw fluid into the barrel. A bulb syringe includes a barrel and an elastic bulb which is squeezed to eject fluid from the barrel and released to draw fluid into the barrel. A variation of the bulb syringe is the bellows syringe in which a bellows is collapsed to eject fluid and allowed to expand to draw fluid into the barrel.

Each of these syringes has advantages and disadvantages. For example, a piston syringe can exert a relatively large force, particularly during suction when the plunger can be manually pulled away from the nozzle or ejector end of the syringe to draw fluid into the barrel. However, a problem with this type of syringe is that too much force may be delivered or provided. Further, the operator must use both hands to return the plunger one hand to grasp the barrel and the other to pull the plunger.

A bulb syringe provides a more gentle suction action but if the nozzle of such a syringe becomes clogged during suction expansion of the bulb will be prevented and a'positive return force cannot be applied by the operator as in the case of a piston syringe.

SUMMARY The inventive syringe combines the advantages of both the piston syringe and the bulb syringe without the attendant disadvantages. The syringe includes a plunger which provides a smooth, continuous ejecting action. As the plunger is depressed, the elastic membrane is stretched and creates a force which acts protectively to restrain delivery of fluid at too rapid a rate. When the pressure on the plunger is released, the elastic membrane provides a relatively mild suction force to return the plunger to its original position while the syringe is held by only one hand. When thesyringe is being used, the

- membrane sealingly engages the walls of the barrel to provide a fluid-tight seal, but when the syringe is not being used, the sealing portion of the membrane rests in a circumferentially enlarged portion of the barrel so that during storage the membrane is not subjected to prolonged compression which could cause permanent deformation or set of the resilient material of the membrane and adversely affect the fluid seal. The inventive syringe can be produced inexpensively enough to allow it to be discarded (and incinerated) after a single use, thereby avoiding the serious problems of cross-contamination which has been found to arise when instruments are re-used, even after supposedly effective sterilizing procedures.

DESCRIPTION OF THE DRAWING The invention will be explained in conjunction withan illustrative embodiment shown in the accompanying drawing in which- FIG. 1 is a perspective view of a syringe formed in accordance with the invention;

FIG. 2 is an enlarged elevational view, partially broken away, of the syringe of FIG. 1;

FIG. 3 is a fragmentary sectional view similar to FIG. 2 showing the plunger being depressed;

FIG. 4 is a sectional view taken along the line 4-4 of FIG.

FIG. 5 is an elevational view, partially broken away, of the elastic membrane;

FIG. 6 is a sectional view taken along the line 6-6 of FIG. 5;

FIG. 7 is a sectional view taken along the line 7-7 of FIG. 5; v

FIG. 8 is a perspective view of a modified syringe; FIG. 9 is an enlarged elevational view, partially broken away, of the syringe of FIG. 8;

FIG. 10 is a fragmentary sectional view similar to FIG. 9 showing the plunger being depressed;

FIG. 11 is a fragmentary view of the lower portion of the plunger;

FIG. 12 is a view similar to FIG. 9 of still another embodiment of the syringe;

FIG. 13 is a sectional view taken along the line l3-13 of FIG. 12;

FIG. 14 is a top plan view of another embodiment of the membrane; and

FIG. 15 is a side view ofthe membrane of FIG. 14.

DESCRIPTION OF SPECIFIC EMBODIMENTS Referring now to the drawing, the numeral 10 designates generally a syringe formed in accordance with the invention which includes an elongated generally tubular barrel 11, a plunger or piston I2, and an elastic membrane 13 interposed therebetween. The particular syringe I0 illustrated is a medical irrigation syringe, but it is to be understood that the invention may be used with other types of syringes.

The barrel I1 includes a generally cylindrical body portion 14 which merges with a generally frustoconical nozzle portion 15 provided with an open end 16 through which fluids may pass. The upper portion of the barrel'includes a radially enlarged cylindrical portion 16 formed concentric with the main body portion 14, and the radially enlarged portion 16 and the body portion 14 merge smoothly and continuously as at 17. The upper end of the barrel II terminates in a radially outwardly extending flange l9, and finger grips 20 extend radially outwardly from the wall of the barrel at generally diametrically opposed locations.

The plunger 12 extends through the open upper end of the barrel 11 and is slidably received therein. The lower end of the plunger 12 terminates in a generally frusto-conical depressor nose portion 21, and the other end terminates in a radially enlarged disc portion 22 adapted to be pressed by the thumb of the operator. The particular plunger illustrated includes a central portion 23 formed of four intersecting planar portions or ribs 23a, 23b, 23c and 23d (FIG. 4) to provide an economical and light yet extremely sturdy plunger. A generally cylindrical end portion 24 joins the central portion 23 to the depressor nose portion 21, and an annular groove 25 (FIG. 2) is provided in portion 24 for cooperation with the membrane as will be explained more fully hereinafter.

The elastic membrane or diaphragm 13 includes a barrel-attaching portion 26 and a plunger portion 27 joined by a plurality of axially extending connecting bands 28. The plunger portion 27 of the membrane includes a generally cylindrical wall portion 29 and terminates in a generally frusto-conical nose 30 which provides an interior cavity 31 shaped to receive the depressor nose 21 of the plunger. A pair of axially spaced circumferentially extending sealing ribs or flanges 32 and 33 extend radially outwardly from the cylindrical wall portion 29 and are constructed and arranged to be compressed by the inner surface of the cylindrical body portion 14 of the barrel to provide a fluid-tight seal therewith. An annular attaching flange 34 extends inwardly from the wall portion 29 generally opposite the upper rib 32 and is received by the annular groove 25 of the plunger to secure the membrane to the plunger.

The barrel-attaching portion 26 of the membrane is seen to be annularly shaped and has a generally C-shaped or U-shaped axial cross section provided by a radially extending lower wall 35, an axially extending outer wall 36, and an upper wall 37 which extends radially inwardly beyond the lower wall 35. As can be seen best in FIG. 2, the annular groove formed by the upper and lower walls of the barrel-attaching portion 26 receives the end flange 19 of the barrel to secure the membrane to the barrel.

The elastic connecting bands 28 of the membrane extend between the plunger portion 27 and the inner edge of the upper wall 37 of the barrel-attaching portion 26, and the particular embodiment illustrated includes four connecting bands spaced 90 apart. It is to be understood, however, that the number and location of the connecting bands can be varied, and the barrel-attaching portion and plunger portion may even be connected by a continuous, generally cylindrical connecting portion.

When the syringe is not being used, the plunger 12 and membrane 13 assume the position shown in FIG. 2. The connecting bands 28 of the membrane are in a relaxed, unstretched state and the sealing ribs 32 and 33 are positioned in the radially enlarged portion 16 of the barrel axially rearwardly of the main body portion 14 of the barrel. In this position the sealing ribs 32 and 33 are not substantially compressed by the wall of the barrel, and the syringe may be stored for a prolonged period of time without causing unnecessary fatigue in the membrane which may affect the fluidtight seal desired.

When the syringe is to be used, the operator grasps the barrel 11 between the fingers of one hand and depresses the plunger 12 by forcing the disc portion 22 downwardly with the thumb, the finger grips permitting the barrel to be firmly held. As the plunger is depressed, the sealing ribs 32 and 33 will move from the radially enlarged portion 16 of the barrel into the more constricted main body portion 14. The smoothly contoured neck portion 17 of the barrel which join the main body and the radially enlarged portion provides a smooth transformation between these portions, and as the membrane moves downwardly, the wall of the main body portion compresses the sealing ribs 32 and 33 to provide a fluid-tight seal. The plunger may be depressed until the desired volume of fluid will be drawn into the barrel upon release of the plunger, and the constricted neck portion 15a joining the main body 14 to the nozzle 15 provides a positive stop to ensure that the connecting bands 28 are not excessively stretched. After the plunger has been depressed the desired distance, the pressure exerted by the thumb may be released, and the stretched elastic connecting bands 28 smoothly return the plunger toward its original position while the syringe is held with one hand. The seal provided by the membrane 13 will provide a gentle sucking action as the plunger returns, and fluid may be drawn into the barrel through the open end 16 of the nozzle.

The fluid may be ejected from the barrel when desired by again depressing the plunger, and the elastic connecting bands 28 provide a force which acts protectively to aid in preventing the fluid from being ejected too fast.

Under ordinary conditions, the syringe requires the use of only a single hand. However, if the nozzle becomes clogged while fluid is being drawn into the barrel or if additional suction force is desired, the plunger can be manually retracted. The membrane is connected to the plunger by the inwardly extending flange 34, and an upward pull on the plunger will also pull the membrane upwardly. The lower wall 35 of the barrel portion of the membrane engages the barrel end flange 35 as the plunger is pulled upwardly, thereby preventing separation of the membrane from the barrel.

Both the barrel 11 and the plunger 12 can advantageously and economically be formed of molded plastic, and the membrane can be molded from a suitable elastic material such as rubber, certain well-known plastics and the like. We have found that syringes formed in accordance with our invention can be produced more inexpensively than many of the syringes heretofore available, and our syringes therefore can be economically disposed of after a single use, thereby eliminating possible cross-contamination if the syringe is used more than once.

If it is desired to use the syringe a number of times, the various parts thereof can easily be separated for cleaning. The membrane can be separated from the barrel merely by flexing the lower wall 35 of the barrel portion 26 outwardly away from the end flange 19 of the barrel. The membrane and plunger can then be withdrawn from the barrel, and cupshaped plunger portion of the membrane can be flexed away from the plunger to withdraw the attaching flange 34 of the membrane from the annular groove 25. Similarly, if the membrane becomes fatigued through excessive use, it can easily be replaced with a new membrane.

A modified syringe 40 is illustrated in FIGS. 8-11 and includes a tubular barrel 41, a plunger or piston 42, and an elastic membrane 43. The barrel 41 is similar to the barrel ll previously described, but the upper portion of barrel 41 is not provided with a radially enlarged end portion.

The plunger 42 includes a disc-like upper end 44, a central portion formed of four intersecting planar portions or ribs .45, and a lower end portion 46. The lower end portion 46 is seen to be generally cylindrical and is provided with an annular groove 47 for cooperation with the membrane. The outer portions of the intersecting ribs are cutaway adjacent the end portion 46 as at 48 to provide shoulders 49.

The membrane 43 is formed of two parts, an elongated elastic band and a plunger portion 51. The ends of the elastic band 50 are provided with suitable openings so that the bands can be attached to the syringe by inserting the end openings of the band over the finger grips 52 of the syringe. The band is also provided with a central opening having a diameter about the same as the distance between diametrically opposed notches 48 in the plunger. The portion of the membrane surrounding the central opening is received between the shoulders 49 and the cylindrical end portion 46 of the plunger and is thereby restrained against axial movement with respect to the plunger 42.

The plunger portion 51 of the membrane is formed separately from the elastic band 50 and is similar to the plunger portion 27 previously described with respect to the membrane 13. The plunger portion 51 includes a generally cylindrical wall portion 53 and terminates in a generally frusto-conical nose 54. A pair of axially spaced circumferentially extending sealing ribs or flanges 55 and 56 extend radially outwardly from the cylindrical wall portion 53 and are constructed and arranged to be compressed by the inner surface of the cylindrical body of the syringe to provide a fluidtight seal therewith. An annular attaching flange 57 extends inwardly from the wall portion 53 generally opposite the upper rib 55 and is received by the annular groove 47 of the plunger to secure the plunger portion 51 t0 the plunger.

When the syringe is not being used, the plunger 42 and elastic band 50 assume the position shown in FIG. 9. As the plunger is depressed as shown in FIG. 10, the central portion of the elastic band 50 is pulled downwardly by the plunger while the end portions of the elastic band remain anchored to the finger grips 52. After the plunger has been depressed the desired distance, the pressure exerted by the operator may be released, and the stretched elastic band 50 will smoothly return the plunger toward its original position while the syringe is held with one hand. The plunger portion 51 provides a seal between the plunger and the barrel as previously discussed as the plunger is depressed and returned.

Referring now to FIG. 12, the syringe includes a barrel 61 and a plunger 62 similar to the barrel and plunger 41' and 42, respectively. The elastic membrane 63 includes a barrel attaching portion 64 and a plunger portion 65 joined by three axially extending elastic connecting bands 66. The plunger portion 65 of the membrane is similar to the plunger portions 51 and 27 hereinbefore described but terminates in an elongated, somewhat bulletshaped projection 67. As the plunger is depressed, the projection 67 will enter the frusto-conical nozzle portion of the barrel and will thereby serve to force a greater amount of fluid from the barrel.

The barrel attaching portion 64 of the membrane is somewhat L-shaped in axial cross section and includes a radially extending annular wall 68 and an axially extending outer wall 69 which extends downwardly along the outer surface of the cylindrical barrel 61. The plunger portion 63 of the membrane is secured to the plunger by an annular attaching flange similar to those previously described.

As the plunger 62 is depressed, the barrel attaching portion 64 secures the upper end of the membrane to the barrel, and the elastic connecting bands 66 will stretch. When the downward force on the plunger is released, the elastic bands will return the plunger to its original position.

Another embodiment of a membrane is shown in FIGS. 14 and 15. The membrane 70 is somewhat similar to the membrane 43 shown in FIGS. 8-10, but the membrane 70 is formed integrally. The membrane 70 is seen to include an elongated band portion 71 having openings 72 in the outer ends thereof and an enlarged generally circular central portion 73 provided with a central opening 74 therethrough. Plunger portion 75 is formed integrally with the band portion 71 and is identical to the plunger portion 51 of membrane 43.

In each of the embodiments the untensioned length of the stretchable portion of the membrane constitutes a minor part of the length of the barrel through which the plunger travels, and the stretched portion will provide a positive return force on the plunger regardless of the distance which the plunger is depressed.

While in the foregoing specification, a detailed description of a specific embodiment of our invention was set forth for the purpose of illustration, it is to be understood that many of the details hereingiven may be varied considerably by those skilled in the art without departing from the spirit and scope of our invention.

We claim:

1. A syringe comprising an elongated barrel having a tubular wall, a plunger longitudinally slidably received by the barrel, and a membrane interposed between the barrel and plunger and sealingly engaging the wall of the barrel, the membrane including a first portion restrained against longitudinal movement by the barrel, a second portion engageable with the plunger for longitudinal movement therewith within the barrel, and a third stretchable elastic portion joining the first and second portions for providing a return force to the second portion and the plunger upon longitudinal movement thereof away from the first portion, the barrel being generally cylindrical and having a plunger end which receives the plunger and an ejector end, the second portion of the membrane providing an elastic sealing portion having a generally circular transverse cross section, the barrel being provided with a diametrically enlarged portion adjacent the plunger end, the sealing portion being sized to be compressed as it moves longitudinally from the diametrically enlarged portion of the barrel toward the ejector end whereby a substantially fluid-tight seal is obtained between the barrel and the plunger.

2. A syringe comprising an elongated barrel having a tubular wall, a plunger longitudinally slidably received by the barrel, and a membrane interposed between the barrel and plunger and sealingly engaging the wall of the barrel, the membrane including a first portion restrained against longitudinal movement by the barrel, a second portion engageable with the plunger for longitudinal movement therewith within the barrel, and a third stretchable elastic portion joining the first and second portions for providing a return force to the second portion and the plunger upon longitudinal movement thereof away from the first portion, the third portion of the membrane comprising a plurality of bands extending longitudinally between the first and second membrane portions at spaced locations around the peripheries thereof.

3. A syringe comprising an elongated barrel having a tubular wall, a plunger longitudinally slidably received by the barrel, and a membrane interposed between the barrel and plunger and sealingly engaging the wall of the barrel, the membrane including a first portion restrained against longitudinal movement by the barrel, a generally cup-shaped second portion receiving an end of the plunger for longitudinal move ment therewith within the barrel, and a third stretchable elastic portion joining the first and second portions for providing a return force to the second portion and the plunger upon longitudinal movement thereof away from the first portion, the plunger including a generally cylindrical portion provided with an annular groove adjacent the end thereof received by the cup-shaped second portion of the membrane, the cupshaped second portion of the membrane including a radially inwardly extending flange received by the annular groove in the plunger whereby the membrane is removably attached to the plunger.

4. A syringe comprising an elongated barrel having a tubular wall, a plunger longitudinally slidably received by the barrel, and a membrane interposed between the barrel and plunger and sealingly engaging the wall of the barrel, the membrane including a first portion restrained against longitudinal movement by the barrel, a second portion engageable with the plunger for longitudinal movement therewith within the barrel, and a third stretchable elastic portion joining the first and second portions for providing a return force to the second portion and the plunger upon longitudinal movement thereof away from the first portion, the second portion of the membrane being generally cup-shaped and receiving an end of the plunger, the cup-shaped membrane portion including a generally cylindrical wall interposed between the plunger and the barrel and having a circumferentially extending sealing rib engaging the barrel.

5. The syringe of claim 4 in which the plunger includes a generally cylindrical portion provided with an annular groove adjacent the end of the plunger received by the cup-shaped membrane portion, the cup-shaped membrane portion including a radially inwardly extending flange received by the annular groove in the plunger whereby the membrane is removably attached to the plunger.

6. An elastic membrane adapted for use in sealingly connecting the barrel and plunger of a syringe comprising an annular barrel-attaching portion having an upper radially extending annular wall and an axially extending outer wall adapted to be positioned along the outside surface of the wall of the barrel, a generally cup-shaped plunger portion adapted to receive an end of the plunger and to be interposed between the plunger and the barrel to provide a substantially fluid-tight seal therebetween, and a plurality of elastic stretchable bands extending between the upper wall of the barrel-attaching portion and the cup-shaped plunger portion.

7. The membrane of claim 6 in which the cup-shaped plunger portion includes a radially inwardly extending attaching flange whereby the membrane may be removably attached to the plunger.

8. The membrane of claim 6 in which the cup-shaped plunger portion includes a radially inwardly extending attaching flange removably attaching the membrane to the plunger and a radially outwardly extending sealing rib for en gaging the barrel.

9. The membrane of claim 6 in which the cup-shaped plunger portion includes a radially outwardly extending sealing rib for engaging the barrel.

10. The membrane of claim 6 in which the cup-shaped plunger portion includes a pair of spaced-apart radially outwardly extending sealing ribs for engaging the barrel.

11. A syringe having a tubular barrel with an open rear end and an orifice at its front end, and a plunger slidably disposed in said barrel and projecting from the open rear end thereof, the improvement wherein a member of stretchable elastic material extends between said barrel and said plunger, said member having a first portion fixed to said barrel adjacent the open rear end thereof, a second portion engaged by the plunger and sealingly engaging the barrel, a third portion comprising a plurality of bands extending longitudinally between the first and second portions of the member, each band having an untensioned length constituting a minor part of the total length of the interior of said barrel and exerting a return force on said plunger when said plunger is urged towards the barrels orifice.

ferential internal enlargement with internal cross-sectional dimensions larger than those of the barrels major portion to receive said third portion of said membrane and relieve compressive forces thereon when said plunger is retracted.

* =1: at at 

1. A syringe comprising an elongated barrel having a tubular wall, a plunger longitudinally slidably received by the barrel, and a membrane interposed between the barrel and plunger and sealingly engaging the wall of the barrel, the membrane including a first portion restrained against longitudinal movement by the barrel, a second portion engageable with the plunger for longitudinal movement therewith within the barrel, and a third stretchable elastic portion joining the first and second portions for providing a return force to the second portion and the plunger upon longitudinal movement thereof away from the first portion, the barrel being generally cylindrical and having a plunger end which receives the plunger and an ejector end, the second portion of the membrane providing an elastic sealing portion having a generally circular transverse cross section, the barrel being provided with a diametrically enlarged portion adjacent the plunger end, the sealing portion being sized to be compressed as it moves longitudinally from the diAmetrically enlarged portion of the barrel toward the ejector end whereby a substantially fluid-tight seal is obtained between the barrel and the plunger.
 2. A syringe comprising an elongated barrel having a tubular wall, a plunger longitudinally slidably received by the barrel, and a membrane interposed between the barrel and plunger and sealingly engaging the wall of the barrel, the membrane including a first portion restrained against longitudinal movement by the barrel, a second portion engageable with the plunger for longitudinal movement therewith within the barrel, and a third stretchable elastic portion joining the first and second portions for providing a return force to the second portion and the plunger upon longitudinal movement thereof away from the first portion, the third portion of the membrane comprising a plurality of bands extending longitudinally between the first and second membrane portions at spaced locations around the peripheries thereof.
 3. A syringe comprising an elongated barrel having a tubular wall, a plunger longitudinally slidably received by the barrel, and a membrane interposed between the barrel and plunger and sealingly engaging the wall of the barrel, the membrane including a first portion restrained against longitudinal movement by the barrel, a generally cup-shaped second portion receiving an end of the plunger for longitudinal movement therewith within the barrel, and a third stretchable elastic portion joining the first and second portions for providing a return force to the second portion and the plunger upon longitudinal movement thereof away from the first portion, the plunger including a generally cylindrical portion provided with an annular groove adjacent the end thereof received by the cup-shaped second portion of the membrane, the cup-shaped second portion of the membrane including a radially inwardly extending flange received by the annular groove in the plunger whereby the membrane is removably attached to the plunger.
 4. A syringe comprising an elongated barrel having a tubular wall, a plunger longitudinally slidably received by the barrel, and a membrane interposed between the barrel and plunger and sealingly engaging the wall of the barrel, the membrane including a first portion restrained against longitudinal movement by the barrel, a second portion engageable with the plunger for longitudinal movement therewith within the barrel, and a third stretchable elastic portion joining the first and second portions for providing a return force to the second portion and the plunger upon longitudinal movement thereof away from the first portion, the second portion of the membrane being generally cup-shaped and receiving an end of the plunger, the cup-shaped membrane portion including a generally cylindrical wall interposed between the plunger and the barrel and having a circumferentially extending sealing rib engaging the barrel.
 5. The syringe of claim 4 in which the plunger includes a generally cylindrical portion provided with an annular groove adjacent the end of the plunger received by the cup-shaped membrane portion, the cup-shaped membrane portion including a radially inwardly extending flange received by the annular groove in the plunger whereby the membrane is removably attached to the plunger.
 6. An elastic membrane adapted for use in sealingly connecting the barrel and plunger of a syringe comprising an annular barrel-attaching portion having an upper radially extending annular wall and an axially extending outer wall adapted to be positioned along the outside surface of the wall of the barrel, a generally cup-shaped plunger portion adapted to receive an end of the plunger and to be interposed between the plunger and the barrel to provide a substantially fluid-tight seal therebetween, and a plurality of elastic stretchable bands extending between the upper wall of the barrel-attaching portion and the cup-shaped plunger portion.
 7. The membrane of claim 6 in which the cup-shaped plunger portion includes a radially inwardly extending attaching flange whereby the membrane may be removably attached to the plunger.
 8. The membrane of claim 6 in which the cup-shaped plunger portion includes a radially inwardly extending attaching flange removably attaching the membrane to the plunger and a radially outwardly extending sealing rib for engaging the barrel.
 9. The membrane of claim 6 in which the cup-shaped plunger portion includes a radially outwardly extending sealing rib for engaging the barrel.
 10. The membrane of claim 6 in which the cup-shaped plunger portion includes a pair of spaced-apart radially outwardly extending sealing ribs for engaging the barrel.
 11. A syringe having a tubular barrel with an open rear end and an orifice at its front end, and a plunger slidably disposed in said barrel and projecting from the open rear end thereof, the improvement wherein a member of stretchable elastic material extends between said barrel and said plunger, said member having a first portion fixed to said barrel adjacent the open rear end thereof, a second portion engaged by the plunger and sealingly engaging the barrel, a third portion comprising a plurality of bands extending longitudinally between the first and second portions of the member, each band having an untensioned length constituting a minor part of the total length of the interior of said barrel and exerting a return force on said plunger when said plunger is urged towards the barrel''s orifice.
 12. The structure of claim 11 in which said barrel has a major portion of its length with internal cross-sectional dimensions slightly less than the maximum cross-sectional dimension of said third portion of said membrane in an uncompressed state, said barrel also having adjacent its open end a circumferential internal enlargement with internal cross-sectional dimensions larger than those of the barrel''s major portion to receive said third portion of said membrane and relieve compressive forces thereon when said plunger is retracted. 